Neanderthals had their own "glue factory"? Archaeologists stumble upon an unexpected discovery in Gibraltar

A recently discovered hearth, apparently dug into the floor of a cave in modern-day Gibraltar, shows that Neanderthals were skilled engineers who mastered the process of making glue. Scientists have found that they used specialized hearths to make resin about 65,000 years ago.

A "glue factory" was discovered on the Iberian Peninsula, which is a carefully designed hearth. According to a new study, this feat was accomplished 20,000 years before modern humans (Homo sapiens) set foot in the region, Live Science reports.

With the help of resin, Neanderthals produced glue, which was used to make weapons and tools. The so-called "factory" allowed Neanderthals to precisely control the fire and regulate the temperature of the flame that produced their sticky creations.

Archaeologists already knew that Neanderthals made glue, including tar and resin, as well as sticky substances from ochre, a reddish mineral that they used for rock art. With these sticky materials, they attached stone blades or points to wooden handles in combination with plant fiber wrappings.

But the latest discovery shows that Neanderthals were skilled engineers who fine-tuned the glue-making process.

"The structure that has revealed a hitherto unknown way by which Neanderthals managed and used fire," the researchers write in the new study.

At first glance, the Neanderthal hearth looks deceptively simple: it is a circular pit, almost 22 centimeters across by 9 centimeters deep, with sharply cut vertical walls. Two short trenches about 2.5 centimeters long extend north and south of the pit. But if the researchers are right, this is a work of precision engineering.

Inside the hearth, the team found traces of charcoal and a partially burnt rockrose, small crystalline lumps of cooled plant resin, and thin twigs from local shrubs. They analyzed samples taken from the blackened walls and floor of the hearth, having found chemicals associated with combustion and residues of protective wax on the leaves of plants. According to the scientists, this hearth - actually more of a buried oven - would have been ideal for heating certain plants to distill tar or resin for making tools.

"To make these so-called glue factories, Neanderthals likely filled the pit with leaves from nearby rockrose plants, which produce a sticky, dark brown resin when heated, the researchers of the new study wrote. Next, they covered the pit with a layer of wet sand and soil, probably mixed with guano to help seal the inside of the pit and keep oxygen out, which would have prevented any flames from burning the contents to a crisp. Finally, they built a small fire on top using thin twigs, which would heat the rockrose leaves in the chamber below," the researchers write in the report.

According to the team, each stage of the process was carefully planned. It's easier to control the temperature of a fire made of thin twigs, and the Neanderthals who used the fire needed to heat the rockrose leaves to about 150 degrees Celsius, but not much higher. And they had to keep the oxygen as far away from the leaves in the pit as possible, as too much oxygen allowed the resin to burn rather than melt.

To investigate this method, the scientists built their own replica of the kiln. During the experiment, the scientists found that the production of the resin may have required the involvement of two people.

"Our colleagues noticed during the experimental archaeology experience that they need to manage the fire covering the plant and also open the crust [the covering over the kiln]," said study co-author Francisco Jiménez-Espejo. He speculated that the two straight channels on either side of the pit could mark where two Neanderthals dug the pit from opposite sides to remove the heated leaves before they cooled. This is because it is difficult to separate the tar from the cooled leaves.

If Neanderthals really worked this way, they were good not only at engineering but also at teamwork.

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